In aluminium production plants, very high amounts of electricity are required for separating alumina into its aluminium and oxygen constituents. Typically, the electricity is fed to the electrodes using a conductor network of large aluminium beams, often having a full rectangular cross-section. These conductor networks are referred to as ‘bus bars’ in the field. An example of such a bus bar conductor network is shown in FIG. 1. It is desirable that the bus bars have a high electrical conductivity—approaching that of a pure aluminium crystal as much as possible—because impurities or irregularities typically negatively affect electrical resistance in the bus bars, which, in turn, results in heat generation and electrical losses. Even small losses can be relatively important due to the massive amounts of electricity being conveyed. Hence, bus bars are often made of relatively pure aluminium from the 1000's series. Use of 1375 aluminium (sometimes referred to as 1370-50), is typical.
Bus bar systems often have complex shapes, and are often made of a plurality of assembled components, including elongated straight portions connected to each other at varying angles with correspondingly large connectors referred to as ‘bus rings’. While elongated straight portions can be cast as a whole, it is often more advantageous to make the connectors or bus rings from stacks of identical plates. These stacks, and the plates forming them, can have various shapes and dimensions, depending of its use in the bus bar network.
Due to the fact that they are not made from a unitary cast block, the bus rings can be the limiting factor in the overall electrical conductivity of the bus bar. The bus ring plates are thus carefully soldered into the assembly with the bus bar portions they interconnect at each end in a manner to obtain high electrical conductivity in the soldered joints, and the bus ring plates are produced in a way to optimize electrical conductivity across both connected ends thereof, while maintaining reasonable production costs. Further, the bus ring plates are typically cut into flat aluminium panels, and because the bus ring plates are used in a stacked arrangement, the planarity and thickness precision of the aluminium panels from which the bus ring plates are made of has an influence of the quality achievable in the soldered bus rings.
In the art, the elongated aluminium panels which could be used to produce plates having characteristics satisfactory for use in bus rings were made by rolling a massive cast block of aluminium, referred to as an ingot, in successive steps, until a long panel having the desired thickness was obtained. The long panel was cut into the elongated aluminium panels, and these thus had standard sizes due to the limited adaptability of the production process. Such aluminium panels made from rolled ingots were used in bus ring plate production, but suffered from some limitations which were tolerated, such as dimensional imprecision in thickness and/or planarity, and the presence of internal stress imparted by the production method, and which negatively affected the later soldering of the plates into a bus ring.
Further, when a producer of bus ring plates received a bus ring plate order, he selected an aluminium panel of one of the standard sizes appropriate to reduce loss, and determined a pattern for the bus ring plates in the aluminium panel with a view to use as much material from the selected aluminium panel. The pattern-making step is referred to in the art as nesting, and was either made manually, for simpler bus ring plate shapes, or by using a dedicated software, such as offered by LANTEC, for example. Nonetheless, there typically resulted an amount of aluminium loss on unused edges of the aluminium panel from the imperfect match between even the most optimal nesting pattern and the closest standard dimensions of the available rolled aluminium panels. There were costs associated with the unused portions of the aluminium plates, and these costs were reflected in the price and availability of bus ring plates.
Henceforth, although known bus ring plate production methods were satisfactory to a certain degree, there remained room for improvement.